Zein appears to function as a N sink for the deposition of nitrogenous compounds in maize. This protein increased preferentialy in endosperms as the rate of N fertilizer increased. The movement of sucrose into kernel is enhanced by a greater capacity to synthesize zein. Thus, the yield response of grain to N fertilizer is enhanced by the presence of a large N sink (zein). SDS-polyacrylamide gel electrophoresis reveals that zein contains principally two components, Z1 (22,00 daltons) and Z2 (19,00 daltons). Mutation at the o2 locus suppresses the synthesis of Z1. When these two zein components were analyzed by isolectric focusing, each contained 3 bands. Analysis of the N-terminus showed that their amino acid sequences were relatively constant. Hybridization of DNA isolated from shoots with cDNA prepared against zein mRNA indicated that zein genes renatured with a rate expected for single-copy sequence. RNA polymerase II from the normal and o2 endosperms have been partially purified. Activity in the developing endosperm of normal kernels was most active at 18 days post-pollination and corresponds to the stage prior to major zein synthesis. Preliminary experiments indicated that the o2 RNA polymerase II differed from the normal enzyme by requiring Mg2 ion for activity.